Heat resistant thermoplastic articles including polyhydroxy polymers

ABSTRACT

Disclosed is a molded or extruded thermoplastic article, including a thermoplastic polyamide composition including (a) a polyamide resin; (b) one or more polyhydroxy polymer(s); (c) one or more co-stabilizer(s); (d) one or more reinforcement agents; (e) and, optionally, a polymeric toughener.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority of U.S. Provisional Application No. 61/137,345, filed on 30 Jul. 2008 and currently pending.

FIELD OF THE INVENTION

The present invention relates to the field of molded and extruded polyamide thermoplastic articles having improved heat stability.

BACKGROUND OF INVENTION

High temperature resins based on polyamides possess desirable chemical resistance, processability and heat resistance. This makes them particularly well suited for demanding high performance automotive and electrical/electronics applications. There is a current and general desire in the automotive field to have heat resistant structures since temperatures higher than 150° C., even higher than 200° C., are often reached in underhood areas of automobiles. When plastic parts are exposed to such high temperatures for a prolonged period, such as in automotive under-the-hood applications or in electrical/electronics applications, the mechanical properties generally tend to decrease due to the thermo-oxidation of the polymer. This phenomenon is called heat aging.

In an attempt to improve heat aging characteristics, it has been the conventional practice to add heat stabilizers (also referred as antioxidants) to thermoplastic polyamide compositions. Examples of such heat stabilizers include hindered phenol antioxidants, amine antioxidants and phosphorus-based antioxidants. For polyamide compositions, three types of heat stabilizers are conventionally used to retain the mechanical properties of the composition upon exposure to high temperatures. One is the use of phenolic antioxidants optionally combined with a phosphorus based synergist as previously mentioned, the use of aromatic amines optionally combined with a phosphorus based synergist and the third one is the use of copper salts and derivatives. Phenolic antioxidants are known to improve the mechanical/physical properties of the thermoplastic composition up to an aging temperature of 120° C.

U.S. Pat. No. 5,965,652 discloses a thermally stable polyamide molding composition containing colloidal copper formed in situ. However, the disclosed compositions exhibit retention of impact strength only for a heat aging at 140° C.

GB patent 839,067 discloses a polyamide composition comprising a copper salt and a halide of a strong organic base. However, the disclosed compositions exhibit improved bending heat stability performance only for a heat aging at 170° C.

Existing technologies lead not only to a poor improvement of long-term heat aging resistance, but also the improved heat aging characteristics are insufficient for more demanding applications involving exposure to higher temperatures such as for example in automotive under-the-hood applications and in electrical/electronics applications.

US 2006/0155034 and US 2008/0146718 patent publications disclose polyamide compositions comprising a metal powder as thermal stabilizer with a fibrous reinforcing agent. Disclosed compositions exhibit improved mechanical properties such as tensile strength and elongation at break upon long-term heat aging at 215° C. However, such metal powders are not only expensive but they are also highly unstable because they are prone to spontaneous combustion.

EP 1041109 discloses a polyamide composition comprising a polyamide resin, a polyhydric alcohol having a melting point of 150 to 280° C., that has good fluidity and mechanical strength and is useful in injection welding techniques.

Unfortunately, with the existing technologies, molded articles based on polyamide compositions either suffer from an unacceptable deterioration of their mechanical properties upon long-term high temperature exposure or they are very expensive due to the use of high-cost heat stabilizers.

There remains a need for low-cost polyamide compositions that are suitable for manufacturing articles and that exhibit good mechanical properties after long-term high temperature exposure.

SUMMARY OF INVENTION

Disclosed is a molded or extruded thermoplastic article, comprising a thermoplastic polyamide composition comprising

-   -   (a) a polyamide resin having a melting point and/or glass         transition;     -   (b) 0.25 to 20 weight percent of one or more polyhydroxy         polymer(s) having a number average molecular weight of at least         2000 and selected from the group consisting of ethylene/vinyl         alcohol copolymer and poly(vinyl alcohol);     -   (c) 0 to 3 weight percent of one or more co-stabilizer(s) having         a 10% weight loss temperature, as determined by         thermogravimetric analysis, of greater than 30° C. below said         melting point of said polyamide resin if said melting point is         present, or at least 250° C. if said melting point is not         present, selected from the group consisting of secondary aryl         amines, hindered amine light stabilizers, hindered phenols, and         mixtures thereof;     -   (d) 10 to about 60 weight percent of one or more reinforcement         agents; and     -   (e) 0 to 20 weight percent of a polymeric toughener comprising a         reactive functional group and/or a metal salt of a carboxylic         acid;         wherein all weight percentages are based on the total weight of         the polyamide composition; and wherein molded 4 mm test bars         prepared from said polyamide composition, and exposed at a test         temperature at 170° C. for a test period of 500 hours, in an         atmosphere of air, and tested according to ISO 527-2/1A, have,         on average, a retention of tensile strength of at least 50         percent, as compared with that of an unexposed control of         identical composition and shape.

Further disclosed is a molded or extruded thermoplastic article, as disclosed above, wherein molded 4 mm test bars prepared from said polyamide composition, and exposed at a test temperature at 210° C. for a test period of 500 hours, in an atmosphere of air, and tested according to ISO 527-2/1A, have, on average, a retention of tensile strength of at least 70 percent, as compared with that of an unexposed control of identical composition and shape.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of the description, unless otherwise specified, “high-temperature” means a temperature at or higher than 170° C., preferably at or higher than 210° C., and most preferably at or higher than 230° C. In the present invention, unless otherwise specified, “long-term” refers to an exposure period equal or longer than 500 hrs, preferably equal or longer than 1000 hrs.

As used herein, the term “high heat stability”, as applied to the polyamide composition disclosed herein or to an article made from the composition, refers to the retention of physical properties (for instance, tensile strength) of 4 mm thick molded test bars consisting of the polyamide composition that are exposed to air oven aging (AOA) conditions in an oven at a test temperature at 170° C. for a test period of at least 500 h, in an atmosphere of air, and then tested according to ISO 527-2/1A method. The physical properties of the test bars are compared to that of unexposed controls that have identical composition and shape, and are expressed in terms of “% retention”. In another preferred embodiment the test temperature is at 210° C., the test period is at 500 hours and the exposed test bars have a % retention of tensile strength of at least 70%. Herein “high heat stability” means that said molded test bars, on average, meet or exceed a retention for tensile strength of 50% when exposed at a test temperature at 170° C. for a test period of at least 500 h. Compositions exhibiting a higher retention of physical properties for a given exposure temperature and time period have better heat stability.

The terms “at 170° C.” and “at 210° C.” refer to the nominal temperature of the environment to which the test bars are exposed; with the understanding that the actual temperature may vary by +/−2° C. from the nominal test temperature.

The term “(meth)acrylate” is meant to include acrylate esters and methacrylate esters.

The polyamide resin used in the present invention has a melting point and/or glass transition. Herein melting points and glass transitions are as determined with differential scanning calorimetry (DSC) at a scan rate of 10° C./min in the first heating scan, wherein the melting point is taken at the maximum of the endothermic peak and the glass transition, if evident, is considered the mid-point of the change in enthalpy.

Polyamides useful in various embodiments are condensation products of one or more dicarboxylic acids and one or more diamines, and/or one or more aminocarboxylic acids, and/or ring-opening polymerization products of one or more cyclic lactams. Suitable cyclic lactams are caprolactam and laurolactam. Polyamides may be fully aliphatic or semi-aromatic.

Fully aliphatic polyamides used in the resin composition of the present invention are formed from aliphatic and alicyclic monomers such as diamines, dicarboxylic acids, lactams, aminocarboxylic acids, and their reactive equivalents. A suitable aminocarboxylic acid is 11-aminododecanoic acid. Suitable lactams are caprolactam and laurolactam. In the context of this invention, the term “fully aliphatic polyamide” also refers to copolymers derived from two or more such monomers and blends of two or more fully aliphatic polyamides. Linear, branched, and cyclic monomers may be used.

Carboxylic acid monomers comprised in the fully aliphatic polyamides include, but are not limited to aliphatic carboxylic acids, such as for example adipic acid (C6), pimelic acid (C7), suberic acid (C8), azelaic acid (C9), decanedioic acid (C10), dodecanedioic acid (C12), tridecanedioic acid (C13), tetradecanedioic acid (C14), and pentadecanedioic acid (C15). Diamines can be chosen among diamines having four or more carbon atoms, including, but not limited to tetramethylene diamine, hexamethylene diamine, octamethylene diamine, decamethylene diamine, dodecamethylene diamine, 2-methylpentamethylene diamine, 2-ethyltetramethylene diamine, 2-methyloctamethylenediamine; trimethylhexamethylenediamine, meta-xylylene diamine, and/or mixtures thereof.

The semi-aromatic polyamide is a homopolymer, a copolymer, a terpolymer or more advanced polymers formed from monomers containing aromatic groups. One or more aromatic carboxylic acids may be terephthalate or a mixture of terephthalate with one or more other carboxylic acids, such as isophthalic acid, phthalic acid, 2-methyl terephthalic acid and naphthalic acid. In addition, the one or more aromatic carboxylic acids may be mixed with one or more aliphatic dicarboxylic acids, as disclosed above. Alternatively, an aromatic diamine such as meta-xylylene diamine (MXD) can be used to provide a semi-aromatic polyamide, an example of which is MXD6, a homopolymer comprising MXD and adipic acid.

Preferred polyamides disclosed herein are homopolymers or copolymers wherein the term copolymer refers to polyamides that have two or more amide and/or diamide molecular repeat units. The homopolymers and copolymers are identified by their respective repeat units. For copolymers disclosed herein, the repeat units are listed in decreasing order of mole % repeat units present in the copolymer. The following list exemplifies the abbreviations used to identify monomers and repeat units in the homopolymer and copolymer polyamides (PA):

-   HMD hexamethylene diamine (or 6 when used in combination with a     diacid) -   T Terephthalic acid -   AA Adipic acid -   DMD Decamethylenediamine -   6     -Caprolactam -   DDA Decanedioic acid -   DDDA Dodecanedioic acid -   I Isophthalic acid -   MXD meta-xylylene diamine -   TMD 1,4-tetramethylene diamine -   4T polymer repeat unit formed from TMD and T -   6T polymer repeat unit formed from HMD and T -   DT polymer repeat unit formed from 2-MPMD and T -   MXD6 polymer repeat unit formed from MXD and AA -   polymer repeat unit formed from HMD and AA -   10T polymer repeat unit formed from DMD and T -   410 polymer repeat unit formed from TMD and DDA -   510 polymer repeat unit formed from 1,5-pentanediamine and DDA -   610 polymer repeat unit formed from HMD and DDA -   612 polymer repeat unit formed from HMD and DDDA -   6 polymer repeat unit formed from     -caprolactam -   11 polymer repeat unit formed from 11-aminoundecanoic acid -   12 polymer repeat unit formed from 12-aminododecanoic acid

Note that in the art the term “6” when used alone designates a polymer repeat unit formed from

-caprolactam. Alternatively “6” when used in combination with a diacid such as T, for instance 6T, the “6” refers to HMD. In repeat units comprising a diamine and diacid, the diamine is designated first. Furthermore, when “6” is used in combination with a diamine, for instance 66, the first “6” refers to the diamine HMD, and the second “6” refers to adipic acid. Likewise, repeat units derived from other amino acids or lactams are designated as single numbers designating the number of carbon atoms.

In one embodiment the polyamide composition comprises a one or more polyamides selected from the group consisting of

-   -   Group (I) Polyamides having said melting point of less than 210°         C., comprising an aliphatic or semiaromatic polyamide selected         from the group poly(pentamethylene decanediamide) (PA510),         poly(pentamethylene dodecanediamide) (PA512),         poly(ε-caprolactam/hexamethylene hexanediamide) (PA6/66),         poly(ε-caprolactam/hexamethylene decanediamide) (PA6/610),         poly(ε-caprolactam/hexamethylene dodecanediamide) (PA6/612),         poly(hexamethylene tridecanediamide) (PA613), poly(hexamethylene         pentadecanediamide) (PA615), poly(ε-caprolactam/tetramethylene         terephthalamide) (PA6/4T), poly(ε-caprolactam/hexamethylene         terephthalamide) (PA6/6T), poly(ε-caprolactam/decamethylene         terephthalamide) (PA6/10T), poly(ε-caprolactam/dodecamethylene         terephthalamide) (PA6/12T), poly(hexamethylene         decanediamide/hexamethylene terephthalamide) (PA610/6T),         poly(hexamethylene dodecanediamide/hexamethylene         terephthalamide) (PA61216T), poly(hexamethylene         tetradecanediamide/hexamethylene terephthalamide) (PA614/6T),         poly(ε-caprolactam/hexamethylene isophthalamide/hexamethylene         terephthalamide) (PA6/6I/6T), poly(ε-caprolactam/hexamethylene         hexanediamide/hexamethylene decanediamide) (PA6/66/610),         poly(ε-caprolactam/hexamethylene hexanediamide/hexamethylene         dodecanediamide) (PA6/66/612), poly(ε-caprolactam/hexamethylene         hexanediamide/hexamethylene decanediamide/hexamethylene         dodecanediamide) (PA6/66/610/612), poly(2-methylpentamethylene         hexanediamide/hexamethylene hexanediamide/hexamethylene         terephthamide) (PA D6/66//6T), poly(2-methylpentamethylene         hexanediamide/hexamethylene hexanediamide/) (PA D6/66),         poly(decamethylene decanediamide) (PA1010), poly(decamethylene         dodecanediamide) (PA1012), poly(decamethylene         decanediamide/decamethylene terephthalamide) (PA1010/10T)         poly(decamethylene decanediamide/dodecamethylene         decanediamide/decamethylene terephthalamide/dodecamethylene         terephthalamide (PA1010/1210/10T/12T),         poly(11-aminoundecanamide) (PA11),         poly(11-aminoundecanamide/tetramethylene terephthalamide)         (PA11/4T), poly(11-aminoundecanamide/hexamethylene         terephthalamide) (PA11/6T),         poly(11-aminoundecanamide/decamethylene terephthalamide)         (PA11/10T), poly(11-aminoundecanamide/dodecamethylene         terephthalamide) (PA11/12T), poly(12-aminododecanamide) (PA12),         poly(12-aminododecanamide/tetramethylene terephthalamide)         (PA12/4T), poly(12-aminododecanamide/hexamethylene         terephthalamide) (PA12/6T),         poly(12-aminododecanamide/decamethylene terephthalamide)         (PA12/10T) poly(dodecamethylene dodecanediamide) (PA1212), and         poly(dodecamethylene dodecanediamide/dodecamethylene         dodecanediamide/dodecamethylene terephthalamide)) (PA1212/12T);     -   Group (II) Polyamides having said melting point of at least 210°         C., and comprising an aliphatic polyamide selected from the         group consisting of poly(tetramethylene hexanediamide) (PA46),         poly(ε-caprolactam) (PA 6), poly(hexamethylene         hexanediamide/(ε-caprolactam/) (PA 66/6) poly(hexamethylene         hexanediamide) (PA 66), poly(hexamethylene         hexanediamide/hexamethylene decanediamide) (PA66/610),         poly(hexamethylene hexanediamide/hexamethylene dodecanediamide)         (PA66/612), poly(hexamethylene hexanediamide/decamethylene         decanediamide) (PA66/1010), poly(hexamethylene decanediarnide)         (PA610), poly(hexamethylene dodecanediamide) (PA612),         poly(hexamethylene tetradecanediamide) (PA614),         poly(hexamethylene hexadecanediamide) (PA616), and         poly(tetramethylene hexanediamide/2-methylpentamethylene         hexanediamide) (PA46/D6);     -   Group (III) Polyamides having said melting point of at least         210° C., and comprising         -   (aa) about 20 to about 35 mole percent semiaromatic repeat             units derived from monomers selected from one or more of the             group consisting of:             -   (i) aromatic dicarboxylic acids having 8 to 20 carbon                 atoms and aliphatic diamines having 4 to 20 carbon                 atoms; and         -   (bb) about 65 to about 80 mole percent aliphatic repeat             units derived from monomers selected from one or more of the             group consisting of:             -   (ii) an aliphatic dicarboxylic acid having 6 to 20                 carbon atoms and said aliphatic diamine having 4 to 20                 carbon atoms; and             -   (iii) a lactam and/or aminocarboxylic acid having 4 to                 20 carbon atoms;     -   Group (IV) Polyamides comprising         -   (cc) about 50 to about 95 mole percent semiaromatic repeat             units derived from monomers selected from one or more of the             group consisting of:             -   (i) aromatic dicarboxylic acids having 8 to 20 carbon                 atoms and aliphatic diamines having 4 to 20 carbon                 atoms; and         -   (dd) about 5 to about 50 mole percent aliphatic repeat units             derived from monomers selected from one or more of the group             consisting of:             -   (ii) an aliphatic dicarboxylic acid having 6 to 20                 carbon atoms and said aliphatic diamine having 4 to 20                 carbon atoms; and             -   (iii) a lactam and/or aminocarboxylic acid having 4 to                 20 carbon atoms;     -   Group (V) Polyamides having said melting point of at least 260°         C., and comprising         -   (ee) greater than 95 mole percent semiaromatic repeat units             derived from monomers selected from one or more of the group             consisting of:             -   (i) aromatic dicarboxylic acids having 8 to 20 carbon                 atoms and aliphatic diamines having 4 to 20 carbon                 atoms; and         -   (ff) less than 5 mole percent aliphatic repeat units derived             from monomers selected from one or more of the group             consisting of:             -   (ii) an aliphatic dicarboxylic acid having 6 to 20                 carbon atoms and said aliphatic diamine having 4 to 20                 carbon atoms;             -   (iii) a lactam and/or aminocarboxylic acid having 4 to                 20 carbon atoms; and     -   Group (VI) Polyamides having no melting point selected from the         group consisting of poly(hexamethylene         isophthalamide/hexamethylene terephthalamide) (6I/6T) and         poly(hexamethylene isophthalamide/hexamethylene         terephthalamide/hexamethylene hexanediamide) (6I/6T/66).

Group (I) Polyamides may have semiaromatic repeat units to the extent that the melting point is less than 210° C. and generally the semiaromatic polyamides of the group have less than 40 mole percent semiaromatic repeat units. Semiaromatic repeat units are defined as those derived from monomers selected from one or more of the group consisting of: aromatic dicarboxylic acids having 8 to 20 carbon atoms and aliphatic diamines having 4 to 20 carbon atoms.

One embodiment is a molded or extruded thermoplastic article wherein said polyamide resin is selected from Group (II) Polyamides and wherein said test temperature is at least 210° C. for a test period of at least 500 hours, and said retention of tensile strength is at least 70 percent, as compared with a non-aged control of identical composition and shape.

Another embodiment is a molded or extruded thermoplastic article wherein said polyamide resin is selected from Group (III) Polyamides selected from the group consisting of poly(tetramethylene hexanediamide/tetramethylene terephthalamide) (PA46/4T), poly(tetramethylene hexanediamide/hexamethylene terephthalamide) (PA46/6T), poly(tetramethylene hexanediamide/2-methylpentamethylene hexanediarnide/decamethylene terephthalamide)_PA46/D6/10T), poly(hexamethylene hexanediamide/hexamethylene terephthalamide) (PA66/6T), poly(hexamethylene hexanediamide/hexamethylene isophthalamide/hexamethylene terephthalamide PA66/6I/6T, and poly(hexamethylene hexanediamide/2-methylpentamethylene hexanediamide/hexamethylene terephthalamide (PA66/D6/6T). A most preferred Group (III) Polyamide is PA 66/6T.

A further preferred embodiment is the molded or extruded thermoplastic article wherein said polyamide resin is selected from Group (III) Polyamides and wherein said test temperature is at least 210° C. for a test period of at least 500 hours, and said retention of tensile strength is at least 70 percent, as compared with a non-aged control of identical composition.

Another embodiment is a molded or extruded thermoplastic article wherein said polyamide resin is selected from Group (IV) Polyamides selected from the group consisting of poly(tetramethylene terephthalamide/hexamethylene hexanediamide) (PA4T/66), poly(tetramethylene terephthalamide/ε-caprolactam) (PA4T/6), poly(tetramethylene terephthalamide/hexamethylene dodecanediamide) (PA4T/612), poly(tetramethylene terephthalamide/2-methylpentamethylene hexanediamide/hexamethylene hexanediamide) (PA4T/D6/66), poly(hexaamethylene terephthalamide/2-methylpentamethylene terephthalamide/hexamethylene hexanediamide) (PA6T/DT/66), poly(hexamethylene terephthalamide/hexamethylene hexanediamide) PA6T/66, poly(hexaamethylene terephthalamide/hexamethylene decanediamide) (PA6T/610), poly(hexamethylene terephthalamide/hexamethylene tetradecanediamide) (PA6T/614), poly(nonamethylene terephthalamide/nonamethylene decanediamide) (PA9T/910), poly(nonamethylene terephthalamide/nonamethylene dodecanediamide) (PA9T/912), poly(nonamethylene terephthalamide/11-aminoundecanamide) (PA9T/11), poly(nonamethylene terephthalamide/12-aminododecanamide) (PA9T/12), poly(decamethylene terephthalamide/11-aminoundecanamide) (PA 10T/11), poly(decamethylene terephthalamide/12-aminododecanamide) (PA10T/12) poly(decamethylene terephthalamide/decamethylene decanediamide) (PA10T/1010), poly(decamethylene terephthalamide/decamethylene dodecanediamide) (PA10T/1012), poly(decamethylene terephthalamide/tetramethylene hexanediamide) (PA10T/46), poly(decamethylene terephthalamide/ε-caprolactam) (PA10T/6), poly(decamethylene terephthalamide/hexamethylene hexanediamide) (PA10T/66), poly(dodecamethylene terephthalamide/dodecamethylene dodecanediamide) (PA12T/1212), poly(dodecamethylene terephthalamide/ε-caprolactam) (PA12T/6), and poly(dodecamethylene terephthalamide/hexamethylene hexanediamide) (PA12T/66); and a most preferred Group (IV) Polyamide is PA6T/66.

A further preferred embodiment is the molded or extruded thermoplastic article wherein said polyamide resin is selected from Group (IV) Polyamides and wherein said test temperature is at least 210° C. for a test period of at least 500 hours and said retention of tensile strength is at least 70%, and more preferably at least 80% and 90%, as compared with a non-aged control of identical composition.

Another embodiment is a molded or extruded thermoplastic article wherein said polyamide resin is selected from Group (V) Polyamides selected from the group consisting of poly(tetramethylene terephthalamide/2-methylpentamethylene terephthalamide) PA4T/DT, poly(tetramethylene terephthalamide/hexamethylene terephthalamide) PA4T/6T, poly(tetramethylene terephthalamide/decamethylene terephthalamide) PA4T/10T, poly(tetramethylene terephthalamide/dodecamethylene terephthalamide)PA4T/12T, poly(tetramethylene terephthalamide/2-methylpentamethylene terephthalamide/hexamethylene terephthalamide) (PA4T/DT/6T), poly(tetramethylene terephthalamide/hexamethylene terephthalamide/2-methylpentamethylene terephthalamide) (PA4T/6T/DT), poly(hexamethylene terephthalamide/2-methylpentamethylene terephthalamide) (PA6T/DT), poly(hexamethylene hexanediamide/hexamethylene isophthalamide) (PA 6T/6I), poly(hexamethylene terephthalamide/decamethylene terephthalamide) PA6T/10T, poly(hexamethylene terephthalamide/dodecamethylene terephthalamide) (PA6T/12T), poly(hexamethylene terephthalamide/2-methylpentamethylene terephthalamide/poly(decamethylene terephthalamide) (PA6T/DT/10T), poly(hexamethylene terephthalamide/decamethylene terephthalamide/dodecamethylene terephthalamide) (PA6T/10T/12T), poly(decamethylene terephthalamide) (PA10T), poly(decamethylene terephthalamide/tetramethylene terephthalamide) (PA10T/4T), poly(decamethylene terephthalamide/2-methylpentamethylene terephthalamide) (PA10T/DT), poly(decamethylene terephthalamide/dodecamethylene terephthalamide) (PA10T/12T), poly(decamethylene terephthalamide/2-methylpentamethylene terephthalamide/(decamethylene terephthalamide) (PA10T/DT/12T). poly(dodecamethylene terephthalamide) (PA12T), poly(dodecamethylene terephthalamide)/tetramethylene terephthalamide) (PA12T/4T), poly(dodecamethylene terephthalamide)/hexamethylene terephthalamide) PA12T/6T, poly(dodecamethylene terephthalamide)/decamethylene terephthalamide) (PA12T/10T), and poly(dodecamethylene terephthalamide)/2-methylpentamethylene terephthalamide) (PA12T/DT); and a most preferred Group (V) Polyamide is PA6T/DT.

A further preferred embodiment is the molded or extruded thermoplastic article wherein said polyamide resin is selected from Group (V) Polyamides and wherein said test temperature is at least 210° C. for a test period of at least 500 hours and said retention of tensile strength is at least 70%, and more preferably at least 80% and 90%, as compared with a non-aged control of identical composition.

In various embodiments the polyamide is a Group (I) Polyamide, Group (II) Polyamide, Group (III) Polyamide, Group (IV) Polyamide, Group (V) Polyamide or Group (VI) Polyamide, respectively.

The polyamides may also be blends of two or more polyamides. Preferred blends include those selected from the group consisting of Group (I) and Group (II) Polyamides; Group (I) and (III) Polyamide, Group (I) and Group (VI) Polyamides, Group (II) and Group (III) Polyamides, Group (II) and Group (IV) Polyamides, Group (II) and (V) Polyamides, Group (II) and Group (VI) Polyamides, Group (III) and Group (VI) Polyamides, and Group (IV) and (V) Polyamides.

A preferred blend includes Group (II) and (V) Polyamides, and a specific preferred blend includes poly(hexamethylene hexanediamide) (PA 66) and poly(hexamethylene terephthalamide/2-methylpentamethylene terephthalamide) (PA 6T/DT).

Another preferred blend includes Group (II) and Group (III) Polyamides and a specific preferred blend includes poly(ε-caprolactam) (PA6) and poly(hexamethylene hexanediamide/hexamethylene terephthalamide (PA66/6T).

Another embodiment is a molded or extruded thermoplastic article comprising a thermoplastic polyamide composition as disclosed above, wherein molded 4 mm test bars prepared from said polyamide composition, and exposed at a test temperature at 210° C. for a test period of 500 hours, in an atmosphere of air, and tested according to ISO 527-2/1A, have, on average, a retention of tensile strength of at least 70 percent, as compared with that of an unexposed control of identical composition and shape. Thermoplastic polyamide compositions meeting these test requirements are referred to as “meeting the requirements of AOA 210° C./500 hours testing.”

The thermoplastic polyamide compositions meeting the requirements of AOA 210° C./500 hours testing comprise one or more polyamide resins wherein said polyamide resin comprises a one or more polyamides independently selected from the groups consisting of Group (II) polyamides, Group (III) Polyamides, Group (IV) Polyamides, Group (V) Polyamides and Group (VI) Polyamides, as disclosed above.

In various embodiments thermoplastic polyamide compositions meeting the requirements of AOA 210° C./500 hours are Group (II) Polyamides, Group (III) Polyamides, Group (IV) Polyamides, Group (V) Polyamides and Group (VI) Polyamides, respectively.

The molded or extruded thermoplastic article comprises 0.25 to 20 weight percent of at least one polyhydroxy polymer having a number average molecular weight (M_(n)) of at least 2000, selected from the group consisting of ethylene/vinyl alcohol copolymer and poly(vinyl alcohol); as determined for polymeric materials with gel permeation chromatography (GPC). Preferably the polyhydroxy polymer has a M_(n) of 5000 to 50,000.

In one embodiment the polyhydroxy polymer is an ethylene/vinyl alcohol copolymer (EVOH). The EVOH may have a vinyl alcohol repeat content of 10 to 90 mol % and preferably 30 to 80 mol %, 40 to 75 mol %, 50 to 75 mol %, and 50 to 60 mol %, wherein the remainder mol % is ethylene. A suitable EVOH for the thermoplastic composition is Soarnol® A or D copolymer available from Nippon Gosei (Tokyo, Japan) and EVAL® copolymers available from Kuraray, Tokyo, Japan.

In one embodiment the polyhydroxy polymer is a poly(vinyl alcohol) polymer (PVOH). Suitable PVOH polymers for the thermoplastic composition are the Mowiol® brand resins available from Kuraray Europe Gmbh.

The molded or extruded thermoplastic article may comprise 1 to 15 weight percent, 1 to 10 weight percent; and preferably 1 to 7 weight percent and more preferably 2 to 7 weight percent polyhydroxy polymer based on the total weight of the thermoplastic polyamide composition.

The polyamide composition may comprise 0 to 3 weight percent of one or more co-stabilizer(s) having a 10% weight loss temperature, as determined by thermogravimetric analysis (TGA), of greater than 30° C. below the melting point of the polyamide resin, if a melting point is present, or at least 250° C. if said melting point is not present, selected from the group consisting of secondary aryl amines, hindered phenols and hindered amine light stabilizers (HALS), and mixtures thereof.

For the purposes of this invention, TGA weight loss will be determined according to ASTM D 3850-94, using a heating rate of 10° C./min, in air purge stream, with an appropriate flow rate of 0.8 mL/second. The one or more co-stabilizer(s) preferably has a 10% weight loss temperature, as determined by TGA, of at least 270° C., and more preferably 290° C., 320° C., and 340° C., and most preferably at least 350° C.

The one or more co-stabilizers preferably are present from at or about 0.1 to at or about 3 weight percent, more preferably at or about 0.1 to at or about 1 weight percent; or more preferably from at or about 0.1 to at or about 0.7 weight percent, based on the total weight of the polyamide composition.

Secondary aryl amines useful in the invention are high molecular weight organic compound having low volatility. Preferably, the high molecular weight organic compound will be selected from the group consisting of secondary aryl amines further characterized as having a molecular weight of at least 260 g/mol and preferably at least 350 g/mol, together with a 10% weight loss temperature as determined by thermogravimetric analysis (TGA) of at least 290° C., preferably at least 300° C., 320° C., 340° C., and most preferably at least 350° C.

By secondary aryl amine is meant an amine compound that contains two carbon radicals chemically bound to a nitrogen atom where at least one, and preferably both carbon radicals, are aromatic. Preferably, at least one of the aromatic radicals, such as, for example, a phenyl, naphthyl or heteroaromatic group, is substituted with at least one substituent, preferably containing 1 to about 20 carbon atoms.

Examples of suitable secondary aryl amines include 4,4′ di(α,α-dimethylbenzyl)diphenylamine available commercially as Naugard 445 from Uniroyal Chemical Company, Middlebury, Conn.; the secondary aryl amine condensation product of the reaction of diphenylamine with acetone, available commercially as Aminox from Uniroyal Chemical Company; and para-(paratoluenesulfonylamido)diphenylamine also available from Uniroyal Chemical Company as Naugard SA. Other suitable secondary aryl amines include N,N′-di-(2-naphthyl)-p-phenylenediamine, available from ICI Rubber Chemicals, Calcutta, India. Other suitable secondary aryl amines include 4,4′-bis(α,α′-tertiaryoctyl)diphenylamine, 4,4′-bis(α-methylbenzhydryl)diphenylamine, and others from EP 0509282 B1. A preferred co-stabilzer for the polyamide composition is a secondary aryl amine.

By hindered phenol is meant an organic compound containing at least one phenol group wherein the aromatic moiety is substituted at least at one and preferably at both positions directly adjacent to the carbon having the phenolic hydroxyl group as a substituent. The substituents adjacent the hydroxyl group are alkyl radicals suitably selected from alkyl groups having from 1 to 10 carbon atoms, and preferably will be tertiary butyl groups. The molecular weight of the hindered phenol is suitably at least about 260, preferably at least about 500, more preferably at least about 600. Most preferred are hindered phenols having low volatility, particularly at the processing temperatures employed for molding the formulations, and may be further characterized as having a 10% TGA weight loss temperature of at least 290° C., preferably at least 300° C., 320° C., 340° C., and most preferably at least 350° C.

Suitable hindered phenol compounds include, for example, tetrakis(methylene(3,5-di-(tert)-butyl-4-hydroxyhydrocinnamate))methane, available commercially as Irganox® 1010 from CIBA Specialty Chemicals, Tarrytown, N.Y. and N,N′-hexamethylene bis (3,5-di-(tert)butyl-hydroxyhydro-cinnamamide) also available from CIBA Specialty Chemicals as Irganox® 1098. Other suitable hindered phenols include 1,3,5-trimethyl-2,4,6tris(3,5-di-(tert)-butyl-4-hydroxybenzyl) benzene and 1,6hexamethylene bis (3,5-di-(tert)butyl4hydroxy hydrocinnamate), both available from CIBA Specialty Chemicals as Irganox® 1330 and 259, respectively. A preferred co-stabilizer for the polyamide composition is a hindered phenol. Irganox 1098 is a most preferred hindered phenol for the compositions.

The hindered amine light stabilizers (HALS) may be one or more hindered amine type light stabilizers (HALS).

HALS are compounds of the following general formulas and combinations thereof:

In these formulas, R₁ up to and including R₅ are independent substituents. Examples of suitable substituents are hydrogen, ether groups, ester groups, amine groups, amide groups, alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, cycloalkyl groups and aryl groups, in which the substituents in turn may contain functional groups; examples of functional groups are alcohols, ketones, anhydrides, imines, siloxanes, ethers, carboxyl groups, aldehydes, esters, amides, imides, amines, nitriles, ethers, urethanes and any combination thereof. A hindered amine light stabilizer may also form part of a polymer or oligomer.

Preferably, the HALS is a compound derived from a substituted piperidine compound, in particular any compound derived from an alkyl-substituted piperidyl, piperidinyl or piperazinone compound, and substituted alkoxypiperidinyl compounds. Examples of such compounds are: 2,2,6,6-tetramethyl-4-piperidone; 2,2,6,6-tetrametyl-4-piperidinol; bis-(1,2,2,6,6-pentamethyl piperidyl)-(3′,5′-di-tert-butyl-4′-hydroxybenzyl) butylmalonate; di-(2,2,6,6-tetramethyl-4-piperidyl) sebacate (Tinuvin® 770, MW 481); oligomer of N-(2-hydroxyethyl)-2,2,6,6-tetramethyl-4-piperidinol and succinic acid (Tinuvin® 622); oligomer of cyanuric acid and N,N-di(2,2,6,6-tetramethyl-4-piperidyl)-hexamethylene diamine; bis-(2,2,6,6-tetramethyl-4-piperidinyl)succinate; bis-(1-octyloxy-2,2,6,6-tetramethyl-4-piperidinyl)sebacate (Tinuvin® 123); bis-(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate (Tinuvin® 765); Tinuvin® 144; Tinuvin® XT850; tetrakis-(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butane tetracarboxylate; N,N′-bis-(2,2,6,6-tetramethyl-4-piperidyl)-hexane-1,6-diamine (Chimasorb® T5); N-butyl-2,2,6,6-tetramethyl-4-piperidinamine; 2,2′-[(2,2,6,6-tetramethyl-piperidinyl)-imino]-bis-[ethanol]; poly((6-morpholine-S-triazine-2,4-diyl)(2,2,6,6-tetramethyl-4-piperidinyl)-iminohexamethylene-(2,2,6,6-tetramethyl-4-piperidinyl)-imino) (Cyasorb® UV 3346); 5-(2,2,6,6-tetramethyl-4-piperidinyl)-2-cyclo-undecyl-oxazole) (Hostavin® N20); 1,1′-(1,2-ethane-di-yl)-bis-(3,3′,5,5′-tetramethyl-piperazinone); 8-acetyl-3-dothecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro(4,5)decane-2, 4-dione; polymethylpropyl-3-oxy-[4(2,2,6,6-tetramethyl)-piperidinyl]siloxane (Uvasil® 299); 1,2,3,4-butane-tetracarboxylic acid-1,2,3-tris(1,2,2,6,6-pentamethyl-4-piperidinyl)-4-tridecylester; copolymer of alpha-methylstyrene-N-(2,2,6,6-tetramethyl-4-piperidinyl) maleimide and N-stearyl maleimide; 1,2,3,4-butanetetracarboxylic acid, polymer with beta,beta,beta′,beta′-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diethanol, 1,2,2,6,6-pentamethyl-4-piperidinyl ester (Mark® LA63); 2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diethanol,beta,beta,beta′,beta′-tetramethyl-polymer with 1,2,3,4-butanetetracarboxylic acid, 2,2,6,6-tetramethyl-4-piperidinyl ester (Mark® LA68); D-glucitol, 1,3:2,4-bis-O-(2,2,6,6-tetramethyl-4-piperidinylidene)-(HALS 7); oligomer of 7-oxa-3,20-diazadispiro[5.1.11.2]-heneicosan-21-one-2,2,4,4-tetramethyl-20-(oxiranylmethyl) (Hostavin® N30); propanedioic acid, [(4-methoxyphenyl)methylene]-, bis(1,2,2,6,6-pentamethyl-4-piperidinyl) ester (Sanduvor® PR 31); formamide, N,N′-1,6-hexanediylbis[N-(2,2,6,6-tetramethyl-4-piperidinyl (Uvinul® 4050H); 1,3,5-triazine-2,4,6-triamine, N,N′″-[1,2-ethanediylbis[[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl) (Chimassorb® 119 MW 2286); poly[[6-[(1,1,3,33-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-peperidinyl)-imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]] (Chimassorb® 944 MW 2000-3000); 1,5-dioxaspiro (5,5) undecane 3,3-dicarboxylic acid, bis(2,2,6,6-tetramethyl-4-peridinyl)ester (Cyasorb® UV-500); 1,5-dioxaspiro (5,5) undecane 3,3-dicarboxylic acid, bis (1,2,2,6,6-pentamethyl-4-peridinyl)ester (Cyasorb® UV-516); N-2,2,6,6-tetramethyl-4-piperidinyl-N-amino-oxamide; 4-acryloyloxy-1,2,2,6,6-pentamethyl-4-piperidine. 1,5,8,12-tetrakis[2′,4′-bis(1″,2″,2″,6″,6″-pentamethyl-4″-piperidinyl(butyl)amino)-1′,3′,5′-triazine-6′-yl]-1,5,8,12-tetraazadodecane; HALS PB-41 (Clariant Huningue S. A.); Nylostab® S-EED (Clariant Huningue S. A.); 3-dodecyl-1-(2,2,6,6-tetramethyl-4-piperidyl)-pyrrolidin-2,5-dione; Uvasorb® HA88; 1,1′-(1,2-ethane-di-yl)-bis-(3,3′,5,5′-tetra-methyl-piperazinone) (Good-rite® 3034); 1,1′1″-(1,3,5-triazine-2,4,6-triyltris((cyclohexylimino)-2,1-ethanediyl)tris(3,3,5,5-tetramethylpiperazinone) (Good-rite® 3150) and; 1,1′,1″-(1,3,5-triazine-2,4,6-triyltris((cyclohexylimino)-2,1-ethanediyl)tris(3,3,4,5,5-tetramethylpiperazinone) (Good-rite® 3159). Tinuvin® and Chimassorb® materials are available from Ciba Specialty Chemicals; Cyasorb® materials are available from Cytec Technology Corp.; Uvasil® materials are available from Great Lakes Chemical Corp.; Saduvor®, Hostavin®, and Nylostab® materials are available from Clariant Corp.; Uvinul® materials are available from BASF; Uvasorb® materials are available from Partecipazioni Industriali; and Good-rite® materials are available from B.F. Goodrich Co. Mark® materials are available from Asahi Denka Co.

A preferred co-stabilizer for the thermoplastic polyamide composition is a HALS. Preferred HALS include high-molecular weight oligomeric or polymeric HALS having a molecular weight of more than about 1000, and preferably more than about 2000.

Other specific HALS are selected from the group consisting or di-(2,2,6,6-tetramethyl-4-piperidyl) sebacate (Tinuvin® 770, MW 481) Nylostab® S-EED (Clariant Huningue S. A.); 1,3,5-triazine-2,4,6-triamine, N,N′″-[1,2-ethanediylbis[[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl) (Chimassorb® 119 MW 2286); and poly[[6-[(1,1,3,33-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-peperidinyl)-imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]] (Chimassorb® 944 MW 2000-3000).

Mixtures of secondary aryl amines and HALS may be used. A preferred embodiment comprises at least two co-stabilizers, at least one selected from the secondary aryl amines; and at least one selected from the group of HALS, as disclosed above, wherein the total weight percent of the mixture of co-stabilizers is at least 0.5 wt percent, and preferably at least 0.9 weight percent.

The molded or extruded thermoplastic article comprises 10 to about 60 weight percent, and preferably about 12.5 to 55 weight percent and 15 to 50 weight percent, of one or more reinforcement agents. The reinforcement agent may be any filler, but is preferably selected from the group consisting calcium carbonate, glass fibers with circular and noncircular cross-section, glass flakes, glass beads, carbon fibers, talc, mica, wollastonite, calcined clay, kaolin, diatomite, magnesium sulfate, magnesium silicate, barium sulfate, titanium dioxide, sodium aluminum carbonate, barium ferrite, potassium titanate and mixtures thereof.

Glass fibers with noncircular cross-section refer to glass fiber having a cross section having a major axis lying perpendicular to a longitudinal direction of the glass fiber and corresponding to the longest linear distance in the cross section. The non-circular cross section has a minor axis corresponding to the longest linear distance in the cross section in a direction perpendicular to the major axis. The non-circular cross section of the fiber may have a variety of shapes including a cocoon-type (figure-eight) shape, a rectangular shape; an elliptical shape; a roughly triangular shape; a polygonal shape; and an oblong shape. As will be understood by those skilled in the art, the cross section may have other shapes. The ratio of the length of the major axis to that of the minor access is preferably between about 1.5:1 and about 6:1. The ratio is more preferably between about 2:1 and 5:1 and yet more preferably between about 3:1 to about 4:1. Suitable glass fiber are disclosed in EP 0 190 001 and EP 0 196 194.

The molded or extruded thermoplastic article, optionally, comprises 0 to 50 weight percent of a polymeric toughener comprising a reactive functional group and/or a metal salt of a carboxylic acid. In one embodiment the molded or extruded thermoplastic article comprises 2 to 20 weight percent polymeric toughener selected from the group consisting of: a copolymer of ethylene, glycidyl(meth)acrylate, and optionally one or more (meth)acrylate esters; an ethylene/α-olefin or ethylene/α-olefin/diene copolymer grafted with an unsaturated carboxylic anhydride; a copolymer of ethylene, 2-isocyanatoethyl(meth)acrylate, and optionally one or more (meth)acrylate esters; and a copolymer of ethylene and acrylic acid reacted with a Zn, Li, Mg or Mn compound to form the corresponding ionomer.

In the present invention, the polyamide composition may also comprise other additives commonly used in the art, such other heat stabilizers or antioxidants, antistatic agents, blowing agents, lubricants, plasticizers, and colorant and pigments.

Other heat stabilizers include copper stabilizers, and mixtures thereof.

A significant advantage of the molded or extruded thermoplastic articles of the invention is that high thermal stability is provided without the use of conventional copper heat stabilizers. Copper heat stabilizers tend to act as corrosive agents over long periods of time at elevated temperatures; and in some environments actually cause degradation of semiaromatic polymers. Thus, another embodiment is molded or extruded thermoplastic article wherein said polyamide composition comprises less than 25 ppm copper as determined with atomic absorption spectroscopy.

Herein the polyamide composition is a mixture by melt-blending, in which all polymeric ingredients are adequately mixed, and all non-polymeric ingredients are adequately dispersed in a polymer matrix. Any melt-blending method may be used for mixing polymeric ingredients and non-polymeric ingredients of the present invention. For example, polymeric ingredients and non-polymeric ingredients may be fed into a melt mixer, such as single screw extruder or twin screw extruder, agitator, single screw or twin screw kneader, or Banbury mixer, and the addition step may be addition of all ingredients at once or gradual addition in batches. When the polymeric ingredient and non-polymeric ingredient are gradually added in batches, a part of the polymeric ingredients and/or non-polymeric ingredients is first added, and then is melt-mixed with the remaining polymeric ingredients and non-polymeric ingredients that are subsequently added, until an adequately mixed composition is obtained. If a reinforcing filler presents a long physical shape (for example, a long glass fiber), drawing extrusion molding may be used to prepare a reinforced composition.

The polyamide composition having a polyhydroxy polymer, as disclosed above, is useful in increasing long-term heat stability at high temperatures of molded or extruded articles made therefrom. The long-term heat stability of the articles can be assessed by exposure (air oven ageing) of 4 mm thick test samples at various test temperatures for various test periods of time. The oven test temperatures for the composition disclosed herein are 170° C. and 500 hours test periods; and 210° C. and 500 hours. The test samples, after air oven ageing, are tested for tensile strength and elongation to break, according to ISO 527-2/1A test method; and compared with unexposed controls having identical composition and shape, that are dry as molded (DAM). The comparison with the DAM controls provides the retention of tensile strength and/or retention of elongation to break, and thus the various compositions can be assessed as to long-term heat stability performance.

In various embodiments the thermoplastic polyamide composition has an AOA 170° C./500 hours retention of tensile strength of at least 50% and preferably at least 60, 70, 80, and 90%, based upon comparison with DAM non-exposed controls.

In various embodiments the thermoplastic polyamide composition has an AOA 210° C./500 hours retention of tensile strength of at least 70% and preferably at least 80, and 90%, based upon comparison with DAM non-exposed controls.

In another aspect, the present invention relates a use of the above disclosed polyamide compositions for high temperature applications.

In another aspect, the present invention relates to a method for manufacturing an article by shaping the thermoplastic composition of the invention. Examples of articles are films or laminates, automotive parts or engine parts or electrical/electronics parts. By “shaping”, it is meant any shaping technique, such as for example extrusion, injection moulding, thermoform moulding, compression moulding or blow moulding. Preferably, the article is shaped by injection moulding or blow moulding.

The molded or extruded thermoplastic articles disclosed herein may have application in many vehicular components that meet one or more of the following requirements: high impact requirements; significant weight reduction (over conventional metals, for instance); resistance to high temperature; resistance to oil environment; resistance to chemical agents such as coolants; and noise reduction allowing more compact and integrated design. Specific molded or extruded thermoplastic articles are selected from the group consisting of charge air coolers (CAC); cylinder head covers (CHC); oil pans; engine cooling systems, including thermostat and heater housings and coolant pumps; exhaust systems including mufflers and housings for catalytic converters; air intake manifolds (AIM); and timing chain belt front covers. As an illustrative example of desired mechanical resistance against long-term high temperature exposure, a charge air cooler can be mentioned. A charge air cooler is a part of the radiator of a vehicle that improves engine combustion efficiency. Charge air coolers reduce the charge air temperature and increase the density of the air after compression in the turbocharger thus allowing more air to enter into the cylinders to improve engine efficiency. Since the temperature of the incoming air can be more than 200° C. when it enters the charge air cooler, it is required that this part be made out of a composition maintaining good mechanical properties under high temperatures for an extended period of time.

The present invention is further illustrated by the following examples. It should be understood that the following examples are for illustration purposes only, and are not used to limit the present invention thereto.

EXAMPLES Methods

Compounding Method A

Examples and Comparative Examples using PA 6T/66 were prepared by melt blending the ingredients listed in the Tables in a 30 mm twin screw extruder (ZSK 30 by Coperion) operating at about 310° C. barrel setting using a screw speed of about 300 rpm, a throughput of 13.6 kg/hour and a melt temperature measured by hand of about 355° C. The glass fibers were added to the melt through a screw side feeder. Ingredient quantities shown in the Tables are given in weight percent on the basis of the total weight of the thermoplastic composition.

The compounded mixture was extruded in the form of laces or strands, cooled in a water bath, chopped into granules and placed into sealed aluminum lined bags in order to prevent moisture pick up. The cooling and cutting conditions were adjusted to ensure that the materials were kept below 0.15 wt % of moisture level.

Compounding Method B

Examples and Comparative Examples using PA 66 and PA 66/6T were prepared by melt blending the ingredients listed in the Tables in a 40 mm twin screw extruder (Berstorff ZE40) operating at about 280° C. using a screw speed of about 300 rpm, a throughput of 110 kg/hour. The glass fibers were added to the melt through a screw side feeder. Ingredient quantities shown in the Tables are given in weight percent on the basis of the total weight of the thermoplastic composition.

The compounded mixture was extruded in the form of laces or strands, cooled in a water bath, chopped into granules and placed into sealed aluminum lined bags in order to prevent moisture pick up. The cooling and cutting conditions were adjusted to ensure that the materials were kept below 0.15 wt % of moisture level.

Physical Properties Measurement

Mechanical tensile properties, i.e. E-modulus, stress at break (Tensile strength) and strain at break (elongation at break) were measured according to ISO 527-2/1A. Measurements were made on injection molded ISO tensile bars. mold temperature for PA 6T/66 test bars was 90-100° C.; and melt temperature was 325-330° C. for both resins. PA 66 and PA 66/6T mold temperature were 100° C., and melt temperatures were 295-300° C.;

The thickness of the test bars was 4 mm and a width of 10 mm according to ISO 527/1A at a testing speed of 5 mm/min (tensile strength and elongation). Tensile Modulus was measured at 1 mm/min.

Air Oven Ageing (AOA)

The test bars were exposed, i.e., heat aged, in a re-circulating air ovens (Heraeus type UT6060) according to the procedure detailed in ISO 2578. At various test times, the test bars were removed from the oven, allowed to cool to room temperature and sealed into aluminum lined bags until ready for testing. The tensile mechanical properties were then measured according to ISO 527 using a Zwick tensile instrument. The average values obtained from 5 specimens are given in the Tables.

Retention of tensile strength (TS) and elongation at break (EL) corresponds to the percentage of the tensile strength and elongation at break after heat aging for 500 hours and 1000 hours in comparison with the value of control bars considered as being 100%. The control bars were of identical compositions and shape to the test bars, but tested dry as molded (DAM) and not subjected to AOA conditions.

Materials

PA66 refers to an aliphatic polyamide made of 1,6-hexanedioic acid and 1,6-hexamethylenediamine having an relative viscosity in the range of 46-51 and a melting point of about 263° C., commercially available from E.I. DuPont de Nemours and Company, Wilmington, Del., USA under the trademark Zytel® 101NC010.

PA 6T/66 refers HTN502 NC010, a copolyamide made from terephthalic acid, adipic acid, and hexamethylenediamine; wherein the two acids are used in a 55:45 molar ratio; having a melting point of ca. 310° C., having an inherent viscosity (IV), according to ASTM D2857 method, in the range of 0.9 to 1.0 (typically 0.96) available from E.I. DuPont de Nemours and Company, Wilmington, Del., USA.

PA66/6T refers to a semiaromatic polyamide made of 1,6-hexanedioic acid and terephthalic acid in a 75/25 molar ratio, respectively, and 1,6-hexamethylenediamine that was provided according to the following procedure: Polyamide 66 salt solution (3928 lbs. of a 51.7 percent by weight with a pH of 8.1) and 2926 lbs of a 25.2% by weight of polyamide 6T salt solution with a pH of 7.6 were charged into an autoclave with 100 g of a conventional antifoam agent, 20 g of sodium hypophosphite, 220 g of sodium bicarbonate, 2476 g of 80% HMD solution in water, and 1584 g of glacial acetic. The solution was then heated while the pressure was allowed to rise to 265 psia at which point, steam was vented to maintain the pressure at 265 psia and heating was continued until the temperature of the batch reached 250° C. The pressure was then reduced slowly to 6 psia, while the batch temperature was allowed to further rise to 280-290° C. The pressure was then held at 6 psia and the temperature was held at 280-290° C. for 20 minutes. Finally, the polymer melt was extruded into strands, cooled, and cut into pellets. The resulting polyamide 66/6T has a melting point of about 268+/−1° C. and a relative viscosity (according to ASTM D-789 method) of 42+/−2.

Glass fibers A 4.5 mm length chopped glass fibers, refers to OCV 983, available from Owens Corning Vetrotex, France.

Glass Fiber D refers to PPG 3540 chopped glass fiber available from PPG Industries, Pittsburgh, Pa.

Soarnol® A refers to an ethylene vinyl alcohol copolymer that has about 56 mol % vinyl alcohol repeat units available from Nippon Gosei (Tokyo, Japan).

Soarnol® D refers to an ethylene vinyl alcohol copolymer that has about 71 mol % vinyl alcohol repeat units available from Nippon Gosei (Tokyo, Japan).

EVAL E105B refers to an ethylene vinyl alcohol copolymer that has about 56 mol % vinyl alcohol repeat units available from Kuraray Co., Ltd of Japan

EVAL F101B refers to an ethylene vinyl alcohol copolymer that has about 68 mol % vinyl alcohol repeat units available from Kuraray Co., Ltd of Japan

Cu heat stabilizer refers to a mixture of 7 parts of potassium iodide and 1 part of copper iodide in 0.5 part of a stearate wax binder.

Naugard® 445 hindered amine refers to 4,4′ di(.α,α-dimethylbenzyl)diphenylamine available commercially from Uniroyal Chemical Company, Middlebury, Conn.

Irganox® 1098 stabilizer was available from Ciba Speciality Chemicals Inc, Tarrytown, N.Y.

Chimassorb® 944 refers to (poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)-imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]]), supplied by Ciba Specialty Chemicals.

Chimassorb® 119 is (1,3,5-triazine-2,4,6-triamine, N,N′″-[1,2-ethanediylbis[[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)), supplied by Ciba Specialty Chemicals.

Black Pigment A refers to 40 wt % nigrosine black pigment concentrate in a PA66 carrier.

Black Pigment B refers to 25 wt % carbon black in a PA6 carrier.

Wax OP is a lubricant manufactured by Clariant Corp., Charlotte, N.C.

Example 1-4 and C-1-C-3

Compositions of Examples 1-4 and Comparative Examples C-1-C-3 are listed in Table 1 for PA6T/66 compositions. Tensile properties after AOA at 210° C. and 230° C. at 500 h and 1000 h, and retention of physical properties are listed in Table 1. Higher values of tensile strength (TS) mean better mechanical properties. Higher % retention of tensile strength indicate a relatively higher thermal stability.

Data in Table 1 shows that Example 1 and 2 having 3 and 6 wt % of Soarnol® D EVOH has a % retention of tensile strength comparable to Comparative Example 1 having a conventional copper stabilizer. Furthermore Example 1 and 2 have significantly higher thermal stability than Comparative Example C-2 having no EVOH.

Examples 3 and 4 having 3 and 6 wt % Soarnol® A EVOH also has % retention of tensile strength comparable to Comparative Example 1. Furthermore Example 3 and 4 have significantly higher thermal stability than Comparative Example C-2 having no EVOH.

These are surprising and unexpected results and demonstrate that the PA6T/66 composition including low levels of an EVOH copolymer can have high heat stability without the use of copper stabilizers.

TABLE 1 Example C-1 C-2 C-3 1 2 3 4 PA6T/66 64.35 63.95 64.25 61.75 58.75 61.75 58.75 Soarnol D 3 6 Soarnol A 3 6 Naugard 445 0.5 Wax OP 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Copper heat stabilizer 0.4 Glass Fiber D 35 35 35 35 35 35 35 AOA 210° C. TS (MPa) 0 h 219 225 208 214 215 215 214 TS (MPa) 500 h 169 112 134 155 161 158 172 TS (MPa) 1000 h 135 89 96 121 128 128 144 500 h TS Retention (%) 77 51 64 72 75 73 80 1000 h TS Retention (%) 62 40 46 57 60 60 67 El (%) 0 h 2.3 2.3 2.2 2.3 2.3 2.3 2.3 El (%) 500 h 1.6 1.3 1.5 1.5 1.6 1.7 1.7 El (%) 1000 h 1.3 1.0 1.2 1.2 1.3 1.2 1.4 500 h El Retention (%) 70 56 68 65 70 74 74 1000 h El Retention (%) 57 43 55 52 57 52 61 AOA 230° C. TS (MPa) 0 h 219 225 208 214 215 215 214 TS (MPa) 500 h 147 83 98 115 125 121 148 TS (MPa) 1000 h 101 76 77 81 92 91 98 500 h TS Retention (%) 67 37 47 54 58 56 69 1000 h TS Retention (%) 46 34 37 38 43 42 46 El (%) 0 h 2.3 2.3 2.2 2.3 2.3 2.3 2.3 El (%) 500 h 1.6 1.0 1.2 1.1 1.3 1.1 1.4 El (%) 1000 h 1.3 0.9 0.9 0.8 1 0.9 1 500 h El Retention (%) 70 56 55 48 57 48 61 1000 h El Retention (%) 57 39 41 35 43 39 43

In all Tables: TS=tensile strength; EL=elongation to break

Example 5-10

Examples 5-10 illustrate the affect of co-stabilizers in combination with EVOH copolymers on the heat stability of PA6T/66 compositions.

Compositions of Examples 5-10, tensile properties after AOA at 210° C. and 230° C. at 500 h and 1000 h, and retention of physical properties are listed in Table 2.

Examples 5-7 show the affect of a secondary aryl amine co-stabilizer in the presence of various levels EVOH on heat stability of PA6T/66 compositions. Examples 5-7 show a % retention of tensile strength at AOA of 210° C./500 h of 83-85% retention; that is significantly higher than that of EVOH alone (Example 1 and 2 show 72-75% retention) and the secondary aryl amine alone (C-3 shows 64% retention).

Examples 8 and 10 indicate that EVOH in the presence of two different co-stabilizers, a secondary aryl amine (Naugard® 445) and a HALS (Chimassorb® stabilizers) show improvement in heat stability over the secondary aryl amine and EVOH alone (Examples 5-7).

Example 9 shows the affect of a hindered phenol in the presence of EVOH.

TABLE 2 Example 5 6 7 8 9 10 PA6T/66 61.25 58.25 55.25 60.55 61.25 60.55 Soarnol ® D 3 6 9 3 3 3 Chimassorb ® 944FDL 0.7 Chimassorb ® 119FL 0.7 Naugard ® 445 0.5 0.5 0.5 0.5 0.5 Wax OP 0.25 0.25 0.25 0.25 0.25 0.25 Irganox ® 1098 0.5 Glass Fiber D 35 35 35 35 35 35 AOA 210° C. TS (MPa) 0 h 212 224 221 202 212 210 TS (MPa) 500 h 178 185 188 182 183 185 TS (MPa) 1000 h 152 162 178 155 162 159 500 h TS Retention (%) 84 83 85 90 86 88 1000 h TS Retention (%) 72 72 81 77 76 76 El (%) 0 h 2.3 2.3 2.3 2.1 2.2 2.2 El (%) 500 h 1.8 1.9 2.1 2 2.1 2 El (%) 1000 h 1.6 1.7 2 1.8 1.8 1.8 500 h El Retention (%) 78 83 91 95 95 91 1000 h El Retention (%) 70 74 87 86 82 82 AOA 230° C. TS (MPa) 0 h 212 224 221 202 212 210 TS (MPa) 500 h 148 161 171 135 155 152 TS (MPa) 1000 h 118 145 162 125 148 125 500 h TS Retention (%) 70 72 77 67 73 72 1000 h TS Retention (%) 56 65 73 62 70 60 El (%) 0 h 2.3 2.3 2.3 2.1 2.2 2.2 El (%) 500 h 1.4 1.5 1.8 1.3 1.5 1.5 El (%) 1000 h 1.3 1.4 1.6 1.2 1.4 1.2 500 h El Retention (%) 61 65 78 62 68 68 1000 h El Retention (%) 57 61 70 57 64 55

Example 11-15

Examples 11-15 illustrate the affect of co-stabilizers in combination with Soarnol® A EVOH copolymers, having 50 to 60 mol % vinyl alcohol repeat units, a preferred embodiment, on the heat stability of PA6T/66 compositions.

Listed in Table 3 are the compositions of Examples 11-15; tensile properties after AOA at 210° C. and 230° C. at 500 h and 1000 h; and the % retention of tensile properties.

Examples 11-13 show the affect of a secondary aryl amine co-stabilizer in the presence of various levels Soarnol® A EVOH on heat stability of PA6T/66 compositions. Examples 11-13 show a % retention of tensile strength, after AOA of 210° C./500 h, of 87-100% retention; that is significantly higher than that of Soarnol® A alone (Example 3 and 4 show 73-80% retention) and the secondary aryl amine alone (C-3 shows 64% retention). These are surprising and unexpected results and show a significant improvement in heat stability over the conventional copper stabilizer illustrated in C-1 (77% retention).

Examples 14 and 15 show the affect of Soarnol® A EVOH in the presence of two different co-stabilizers, a secondary aryl amine (Naugard® 445) and a HALS (Chimassorb® stabilizers).

TABLE 3 Example 11 12 13 14 15 PA 6T/66 61.25 58.25 55.25 60.55 60.55 Chimassorb ® 944FDL 0.7 Soarnol ® A 3 6 9 3 3 Chimassorb ® 119FL 0.7 Naugard ® 445 0.5 0.5 0.5 0.5 0.5 Wax OP 0.25 0.25 0.25 0.25 0.25 Glass Fiber D 35 35 35 35 35 AOA 210° C. TS (MPa) 0 h 214 207 206 216 215 TS (MPa) 500 h 186 206 206 188 192 TS (MPa) 1000 h 161 202 205 170 168 500 h TS Retention (%) 87 100 100 87 89 1000 h TS Retention (%) 75 98 100 79 78 El (%) 0 h 2.2 2.4 2.4 2.2 2.1 El (%) 500 h 1.9 2.5 2.5 2.1 2 El (%) 1000 h 1.7 2.4 2.4 2 1.9 500 h El Retention (%) 86 104 104 95 95 1000 h El Retention (%) 77 100 100 91 90 AOA 230° C. TS (MPa) 0 h 214 207 206 216 215 TS (MPa) 500 h 151 193 196 155 161 TS (MPa) 1000 h 131 185 183 129 135 500 h TS Retention (%) 71 93 95 72 75 1000 h TS Retention (%) 61 89 89 60 63 El (%) 0 h 2.2 2.4 2.4 2.2 2.1 El (%) 500 h 1.5 2.3 2.3 1.5 1.5 El (%) 1000 h 1.3 2.1 2.1 1.3 1.3 500 h El Retention (%) 68 96 96 68 71 1000 h El Retention (%) 59 88 88 59 62

Example 16 and C-4 and C-5

Compositions of Examples 16 and Comparative Examples C-4 and C-5 are listed in Table 4 for PA66 compositions. Tensile properties after AOA at 210° C. at 500 h and 1000 h, and retention of physical properties are listed in Table 4. Example 16 shows that 5 wt % EVOH in PA 66 provides significant improvement in % retention of tensile strength as compared to that of C-4 having no EVOH, or C-5 having a conventional copper stabilizer.

TABLE 4 Example C-4 C-5 16 PA 66 70.00 63.50 58.80 Glass fiber A 30.00 35.00 35.00 Black Pigment B 0.60 0.60 Black Pigment A 0.60 0.60 Copper heat stabilizer 0.30 EVAL E105B 5.00 Tensile properties DAM Tensile Modulus [MPa] 9385.0 11129 11569 Tensile Strength [MPa] 199.8 226.8 219.6 Elongation @ Break [%] 3.9 3.4 3.3 AOA 500 h at 210° C. Tensile Modulus [MPa] 9810.2 11137 11339 Tensile Strength [MPa] 94.2 134.7 165.8 retention TS (%) 47.2 59.4 75.5 Elongation @ Break [%] 1.2 1.4 1.8 AOA 1000 h at 210° C. Tensile Modulus [MPa] 5123 6775 7074 Tensile Strength [MPa] 12.8 70.0 56.0 retention TS (%) 6.4 30.9 25.5 Elongation @ Break [%] 0.3 1.5 1.1

Example 17-19 and C-6

Compositions of Examples 17-19 and Comparative Examples C-6 are listed in Table 5 for PA66/6T compositions. Tensile properties after AOA at 210° C. and 230° C. at 500 h and 1000 h, and retention of physical properties are listed in Table 5.

Example 17 and 18 shows that 5 wt % EVOH in PA66/6T provides comparable % retention of tensile strength as compared to that of C-6 having a conventional copper stabilizer. Furthermore, Example 19 shows the affect of a secondary aryl amine co-stabilizer in the presence of EVOH. Example 19 shows a significant and surprising improvement in heat stability over that of the conventional copper stabilized composition (C-5); and over Examples 17 and 18 containing only EVOH as a stabilizer.

TABLE 5 Example C-6 17 18 19 PA 66/6T 68.85 58.80 58.80 58.30 Glass fiber A 30.00 35.00 35.00 35.00 Black Pigment B 0.60 0.60 0.60 Black Pigment A 0.70 0.60 0.60 0.60 Copper heat stabilizer 0.45 EVAL E105B 5.00 5.00 EVAL F101B 5.00 Naugard ® 445 0.50 Tensile properties DAM Tensile Modulus 8791 10583 10745 10814 [MPa] Tensile Strength 198.6 214.7 216.0 212.3 [MPa] Elongation @ Break 3.7 3.6 3.5 3.6 [%] AOA 500 h at 210° C. Tensile Modulus 8353 10489 10887 10762 [MPa] Tensile Strength 148.0 158.9 157.3 204.6 [MPa] retention TS (%) 74.5 74.0 72.8 96.4 Elongation @ Break 1.9 1.8 1.7 2.7 [%] AOA 1000 h at 210° C. Tensile Modulus 9142 8479 9161 10655 [MPa] Tensile Strength 86.0 56.0 62.0 146.0 [MPa] retention TS (%) 43.3 26.1 28.7 68.8 Elongation @ Break 1.1 0.8 0.8 1.7 [%] 

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 16. A molded or extruded thermoplastic article, comprising a thermoplastic polyamide composition comprising (a) a polyamide resin having a melting point and/or glass transition temperature; (b) 1 to 10 weight percent of one or more polyhydroxy polymer(s) having a number average molecular weight of at least 2000 and selected from the group consisting of ethylene/vinyl alcohol copolymers; (c) 0.1 to 3 weight percent of one or more co-stabilizer(s) having a 10% weight loss temperature, as determined by thermogravimetric analysis, of greater than 30° C. below said melting point of said polyamide resin if said melting point is present, or at least 250° C. if said melting point is not present, selected from the group consisting of secondary aryl amines, hindered amine light stabilizers, hindered phenols, and mixtures thereof; (d) 10 to about 60 weight percent of one or more reinforcement agents; and (e) 0 to 20 weight percent of a polymeric toughener comprising a reactive functional group and/or a metal salt of a carboxylic acid; wherein all weight percentages are based on the total weight of the polyamide composition; wherein molded 4 mm test bars prepared from said polyamide composition, and exposed at a test temperature at 170° C. for a test period of 500 hours, in an atmosphere of air, and tested according to ISO 527-2/1A, have, on average, a retention of tensile strength of at least 50 percent, as compared with that of an unexposed control of identical composition and shape; and wherein said polyamide resin is selected from Group (II) Polyamides having said melting point of at least 210° C., and comprising an aliphatic polyamide selected from the group consisting of poly(tetramethylene hexanediamide) (PA46), poly(s-caprolactam) (PA 6), poly(hexamethylene hexanediannide/-(ε-caprolactam/) (PA 6616) poly(hexamethylene hexanediamide) (PA 66), poly(hexamethylene hexanediamide/hexamethylene decanediamide) (PA66/610), poly(hexamethylene hexanediamide/hexamethylene dodecanediamide) (PA66/612), poly(hexamethylene hexanediamide/decamethylene decanediamide) (PA66/1010), poly(hexamethylene decanediamide) (PA610), poly(hexamethylene dodecanediamide) (PA612), poly(hexamethylene tetradecanediamide) (PA614), poly(hexamethylene hexadecanediamide) (PA616), and poly(tetramethylene hexanediarnide/2-methylpentamethylene hexanediamide) (PA46/D6).
 17. The molded or extruded thermoplastic article of claim 16 wherein said polyamide resin additionally comprises a polyamide selected from the group consisting of Group (III) Polyamides, Group (IV) Polyamides, Group (V) Polyamides, and Group (VI) Polyamides, wherein Group (III) Polyamides have a melting point of at least 210° C., and comprise (aa) about 20 to about 35 mole percent semiaromatic repeat units derived from monomers selected from one or more of the group consisting of: i. aromatic dicarboxylic acids having 8 to 20 carbon atoms and aliphatic diamines having 4 to 20 carbon atoms; and (bb) about 65 to about 80 mole percent aliphatic repeat units derived from monomers selected from one or more of the group consisting of: ii. an aliphatic dicarboxylic acid having 6 to 20 carbon atoms and said aliphatic diamine having 4 to 20 carbon atoms; and iii. a lactam and/or aminocarboxylic acid having 4 to 20 carbon atoms; and Group (IV) Polyamides comprising (cc) about 50 to about 95 mole percent semiaromatic repeat units derived from monomers selected from one or more of the group consisting of: i) aromatic dicarboxylic acids having 8 to 20 carbon atoms and aliphatic diamines having 4 to 20 carbon atoms; and (dd) about 5 to about 50 mole percent aliphatic repeat units derived from monomers selected from one or more of the group consisting of: ii) an aliphatic dicarboxylic acid having 6 to 20 carbon atoms and said aliphatic diamine having 4 to 20 carbon atoms; and iii) a lactam and/or aminocarboxylic acid having 4 to 20 carbon atoms; Group (V) Polyamides have a melting point of at least 260° C., and comprising (ee) greater than 95 mole percent semiaromatic repeat units derived from monomers selected from one or more of the group consisting of: ii) aromatic dicarboxylic acids having 8 to 20 carbon atoms and aliphatic diamines having 4 to 20 carbon atoms; and (ff) less than 5 mole percent aliphatic repeat units derived from monomers selected from one or more of the group consisting of: ii) an aliphatic dicarboxylic acid having 6 to 20 carbon atoms and said aliphatic diamine having 4 to 20 carbon atoms; and iii) a lactam and/or aminocarboxylic acid having 4 to 20 carbon atoms; and Group (VI) polyamides have melting point, and selected from the group consisting of poly(hexamethylene isophthalamide/hexamethylene terephthalamide) (6I/6T) and poly(hexamethylene isophthalamide/hexamethylene terephthalamide/hexamethylene hexanediamide) (61/61/66).
 18. The molded or extruded thermoplastic article of claim 16 wherein said one or more co-stabilizer(s) is present at 0.1 to about 3 weight percent.
 19. The molded or extruded thermoplastic article of claim 17 wherein said polyamide resin comprises said Group (II) and Group (V) Polyamides.
 20. The molded or extruded thermoplastic article of claim 17 wherein said polyamide resin comprises said Group (II) and Group (III) Polyamides.
 21. The molded or extruded thermoplastic article of claim 16 wherein the one or more polyhydroxy polymer(s) comprises an ethylene/vinyl alcohol copolymer and has a vinyl alcohol content of 40 to 75 mol %, wherein the remainder mol % is ethylene.
 22. The molded or extruded thermoplastic article of claim 16 wherein the at least one co-stabilizer is one or more secondary aryl amines.
 23. The molded or extruded thermoplastic article of claim 16 wherein the at least one co-stabilizer is one or more hindered amine light stabilizers.
 24. The molded or extruded thermoplastic article of claim 16 wherein the at least one co-stabilizer is one or more hindered phenols.
 25. The molded or extruded thermoplastic article of claim 16 wherein said thermoplastic polyamide composition comprises less than 25 ppm copper as determined with atomic absorption spectroscopy
 26. The molded or extruded thermoplastic article of claim 16 selected from the group consisting of charge air coolers; cylinder head covers; oil pans; engine cooling systems, thermostat and heater housings, coolant pumps, mufflers, housings for catalytic converters; air intake manifolds; and timing chain belt front covers.
 27. A molded or extruded thermoplastic article, comprising a thermoplastic polyamide composition comprising a) a polyamide resin having a melting point and/or glass transition temperature; b) 1 to 10 weight percent of one or more polyhydroxy polymer(s) having a number average molecular weight of at least 2000 and selected from the group consisting of ethylene/vinyl alcohol copolymers; c) 0.1 to 3 weight percent of one or more co-stabilizer(s) having a 10% weight loss temperature, as determined by thermogravirnetric analysis, of greater than 30° C. below said melting point of said polyamide resin if said melting point is present, or at least 250° C. if said melting point is not present, selected from the group consisting of secondary aryl amines, hindered amine light stabilizers, hindered phenols, and mixtures thereof; d) 10 to about 60 weight percent of one or more reinforcement agents; and e) 0 to 20 weight percent of a polymeric toughener comprising a reactive functional group and/or a metal salt of a carboxylic acid; wherein all weight percentages are based on the total weight of the polyamide composition; and wherein molded 4 mm test bars prepared from said polyamide composition, and exposed at a test temperature at 210° C. for a test period of 500 hours, in an atmosphere of air, and tested according to ISO 527-2/1A, have, on average, a retention of tensile strength of at least 70 percent, as compared with that of an unexposed control of identical composition and shape; and wherein said polyamide resin is selected from Group (II) Polyamides having said melting point of at least 210° C., and comprising an aliphatic polyamide selected from the group consisting of poly(tetramethylene hexanediamide) (PA46), poly(ε-caprolactam) (PA 6), poly(hexamethylene hexanediamide/(ε-caprolactam/) (PA 66/6) poly(hexamethylene hexanediamide) (PA 66), poly(hexamethylene hexanediamide/hexamethylene decanediamide) (PA66/610), poly(hexamethylene hexanediamide/hexamethylene dodecanediamide) (PA661612), poly(hexamethylene hexanediamide/decamethylene decanediamide) (PA66/1010), poly(hexamethylene decanediamide) (PA610), poly(hexamethylene dodecanediamide) (PA612), poly(hexamethylene tetradecanediamide) (PA614), poly(hexamethylene hexadecanediamide) (PA616), and poly(tetramethylene hexanediamide/2-methylpentamethylene hexanediamide) (PA46/D6). 